1. Field of the Invention
The present invention relates to a connection apparatus for connecting a digital or analog subscriber line of a communication network to a communication device of a subscriber.
2. Description of the Related Art
When a subscriber of a digital communication network such as an ISDN wants to connect his/her analog communication device to the digital communication network, the analog communication terminal must be connected to the subscriber line of the digital communication network through a terminal adapter (TA).
The TA has, as an interface to a personal computer, a digital port such as RS-232C, a digital port (S/T point interface in an ISDN) for connecting a digital device such as a digital telephone, and an analog port (modular jack) for connecting a conventional analog telephone or G3-FAX. Some TAs have a plurality of analog ports. With the use of TA, two arbitrary types of communication/speech communication selected from personal computer communication, digital telephone, analog telephone, FAX, and the like can be performed through an ISDN.
FIG. 1 shows the connection form of a general TA. Reference numeral 100 denotes a TA for transmitting/receiving data/speech data to/from a digital communication line such as an ISDN via a line interface; 102, a digital port connected to a personal computer; 103, a digital port connected to a digital communication device such as a digital telephone; 104, an analog port connected to an analog telephone or FAX; and 105, an analog port like the analog port 104. In this example, the TA has two analog ports.
In the arrangement shown in FIG. 1, when the digital line is used, the communication rate of personal computer communication can be raised, and additionally, a telephone or FAX can be used while performing personal computer communication.
The TA shown in FIG. 1 is connected to one ISDN line having two communication channels. Some private branch exchanges (including key telephones) allow 2.times.n terminals to simultaneously communicate by connecting a plurality of (n) ISDN lines.
Some other private branch exchanges are connected to both a digital line such as an ISDN line and an analog line.
One of the convenient functions of such communication is a calling party number notification (caller ID) function. Upon reception of an incoming call, this function serves to notify the called party of the telephone number of the caller and is effectively used to avoid unwanted calls.
The ISDN as a digital network has long supported this calling party number notification function. For example, the INS 64 service of NTT is providing this function free. Most digital devices such as a digital telephone that are connected to the ISDN are compatible with this function. These devices include displays such as LCDs (liquid crystal displays) and have functions of displaying the calling party number upon reception of an incoming call and storing this calling party number to use as data for redialing.
The PSTN (Public Switched Telephone Network) as an analog network is already providing this service in USA, Canada, or England. Even in Japan, this service is planned to start soon, and analog telephones for PSTN are being developed.
However, although the above-described general TA or private branch exchange has an analog port for connecting an analog device, the analog device connected to the analog port is not notified of the calling party number.
For this reason, even when an analog device having an existing calling party number notification function is connected, this function is wasteful, and the existing resource cannot be effectively used.
Conversely, even when a PSTN line as an analog line and an ISDN terminal as a digital terminal are connected to a private branch exchange, the ISDN terminal is not notified of the calling party number which has been notified from the PSTN line upon reception of an incoming call.